REDR2002 Reproduction in Domestic Ruminants V Neuroendocrine Interactions (4 abstracts)
Sexually differentiated regulation of GnRH release by gonadal steroid hormones in sheep
JE Robinson 1 , RA Birch 2 , JAE Grindrod 1 , JA Taylor 1 & WP Unsworth 1
1Laboratory of Neuroendocrinology, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK; and 2Department of Reproductive Science and Medicine, Imperial College School of Medicine, Hammersmith Hospital, London W12 OHS, UK
Exposure of Ihe sheep fetus to testosterone from day 30 to day 90 of a 147 day gestation causes the neurones that control GnRH secretion, the GnRH neuronal network, to become organized in a sex-specific manner. After androgen exposure in utero, GnRH neurones are activated in a sexually differentiated pattern by gonadal steroid hormones. Specifically, follicular phase concentrations of oestrogen trigger a GnRH 'surge' in ewes, but not in rams or females treated with androgen during fetal life. Furthermore, progesterone is a less potent inhibitor of GnRH release in rams or females treated with androgen during fetal life. The reasons for the sexual differentiation of these steroid feedback mechanisms probably reside in a dimorphism in steroid-sensitive neural inputs to GnRH neurones. The density of neurones containing oestrogen receptor α is sexually differentiated in areas of the ovine brain that are known to be involved in the steroidal regulation of GnRH. Furthermore, neurones in these regions are activated in a gender-specific pattern. A determination of the neural phenotype of these steroid-sensitive cells will form a basis for understanding the mechanisms by which the GnRH neuronal network is organized and activated in a sexually differentiated manner.
© 2003 Society for Reproduction and Fertility
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